1. Technical Field
The present invention relates to a light emitting module and a display device having the light emitting module, and more particularly, to a light emitting module capable of enhancing light emitting efficiency to obtain white light a display device having the light emitting module.
2. Discussion of the Related Art
A display apparatus includes a backlight assembly providing light to a display panel to display an image. A light source used for the backlight assembly includes a cold cathode fluorescent lamp (CCFL), and a light emitting diode (LED) having low power consumption, low volume and low weight. The LED is widely used for the light source of the backlight assembly due to efficiency of the LED
The backlight assembly emits white light for a liquid crystal display (LCD) apparatus to display the image. Red light, green light and blue light emitted from a red LED, a green LED and a blue LED are mixed to be the white light, to enhance light reproducibility of the image displayed by the LCD apparatus. The white light passes through a liquid crystal layer to control the light intensity, and the white light passes through a color filter to display the color of each pixel.
Light-electrical efficiency of the LED may be different according to a structure of a light emitting chip and a packaging method, but wavelengths of the red light, the green light and the blue light may be about 625 nm, about 525 nm and about 455 nm, respectively. The red, green and blue LEDs respectively have light intensities of about 40 lm/W, about 45 lm/W and about 10 lm/W in the same condition, such as unit power consumption and unit light emitting area.
When the red light, the green light and the blue light are mixed with a ratio of 3:6:1 with respect to the light intensity to be the white light, the red LED and the blue LED may respectively emit about 30 lm red light and about 10 lm blue light, but the green LED only emits about 45 lm in the condition of the unit power consumption and the unit light emitting area. Thus, the light intensity of the green light is insufficient to emit the white light. Two green LEDs can be used in an R, G, G, B array to increase the light intensity of the green light.
The light-electrical efficiency of the LED is continuously enhanced to meet the light intensity to emit the white light. The wavelength of the blue light is preferable to be close to about 450 nm than the present wavelength which is about 455 nm to enhance the light-electrical efficiency of the LED and the light reproducibility. When the wavelength of the blue light is about 450 nm or lower than about 450 nm, the light intensity of the blue light may be insufficient to emit the white light. Alternatively, the light intensity of the red light may be insufficient to emit the white light.
The red, green and blue LEDs having substantially same light emitting area are used to emit the white light. However, since the light-electrical efficiency of the LEDs are continuously enhanced as mentioned above, when the red, green and blue LEDs having the same light emitting area are used, at least one of the red, green and blue LEDs may have the light emitting area smaller or larger than the light emitting area required to emit the white light. Thus, light emitting efficiency is decreased, so that the backlight module is designed considering the light-electrical efficiency of the LED and the light emitting area required to emit the white light.